[pushed][LRA]: Exclude reloading of frame pointer in subreg for some cases

[pushed][LRA]: Exclude reloading of frame pointer in subreg for some cases

[Vladimir Makarov]

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The following patch improves code for avr LRA port.  More explanation 
for the patch can be found in the commit message.

The patch was successfully bootstrapped and tested on x86-64, aarch64, 
and ppc64le.

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commit 4b8878fbf7b74ea5c3405c9f558df0517036f131
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Thu Jul 20 14:34:26 2023 -0400

    [LRA]: Exclude reloading of frame pointer in subreg for some cases
    
    LRA for avr port reloads frame pointer in subreg although we can just
    simplify the subreg.  It results in generation of bad performance code.  The following
    patch fixes this.
    
    gcc/ChangeLog:
    
            * lra-constraints.cc (simplify_operand_subreg): Check frame pointer
            simplification.

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 76a155e99c2..f3784cf5a5b 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -1797,6 +1797,16 @@ simplify_operand_subreg (int nop, machine_mode reg_mode)
       alter_subreg (curr_id->operand_loc[nop], false);
       return true;
     }
+  auto fp_subreg_can_be_simplified_after_reload_p = [] (machine_mode innermode,
+							poly_uint64 offset,
+							machine_mode mode) {
+    reload_completed = 1;
+    bool res = simplify_subreg_regno (FRAME_POINTER_REGNUM,
+				      innermode,
+				      offset, mode) >= 0;
+    reload_completed = 0;
+    return res;
+  };
   /* Force a reload of the SUBREG_REG if this is a constant or PLUS or
      if there may be a problem accessing OPERAND in the outer
      mode.  */
@@ -1809,6 +1819,12 @@ simplify_operand_subreg (int nop, machine_mode reg_mode)
 	   >= hard_regno_nregs (hard_regno, mode))
        && simplify_subreg_regno (hard_regno, innermode,
 				 SUBREG_BYTE (operand), mode) < 0
+       /* Exclude reloading of frame pointer in subreg if frame pointer can not
+	  be simplified here only because the reload is not finished yet.  */
+       && (hard_regno != FRAME_POINTER_REGNUM
+	   || !fp_subreg_can_be_simplified_after_reload_p (innermode,
+							   SUBREG_BYTE (operand),
+							   mode))
        /* Don't reload subreg for matching reload.  It is actually
 	  valid subreg in LRA.  */
        && ! LRA_SUBREG_P (operand))